In general, a front fork interposed between a chassis and an axle of a saddle type vehicle such as a motorcycle includes a telescopic fork body having an outer tube and an inner tube inserted into the outer tube in an axial direction such that they can move relatively, and a damper housed in the fork body. The damper expands and retracts along with the fork body to produce a damping force, and this damping force dampens a vibration of the chassis.
In the front fork described above, the fork body internally has a suspension spring that biases the fork body in an expansion direction so that a weight of the chassis is elastically supported by the suspension spring. In recent years, a light-weight front fork has been developed, in which an air spring is employed as the suspension spring (for example, refer to JP 2010-164167 A and JP 2011-252590 A).
In the front fork including an air spring as a suspension spring as described above, if a gas leaks out of the fork body, the spring force exerted by the air spring for supporting the chassis is eliminated. Therefore, it is important to hermetically seal the fork body.
In an inner circumference of the outer tube, there is installed a cylindrical bushing that makes sliding contact with the inner tube to guide movement of the inner tube relative to the outer tube in an axial direction. For lubricating the bushing, a lubricant is filled in a gap between the inner tube and the outer tube.
For this reason, the front fork described above includes an annular dust seal held in an inner circumference of the outer tube to make sliding contact with an outer circumference of the inner tube, and an annular oil seal held in the inner circumference of the outer tube to be inner than the dust seal inside the fork body and make sliding contact with the outer circumference of the inner tube.
The oil seal scrapes off the lubricant adhering to the outer circumference of the inner tube to prevent the lubricant and the gas from leaking out of the fork body. The dust seal scrapes off a foreign object such as dust, mud, and water adhering to the outer circumferential surface of the inner tube to prevent a foreign object from being mixed inside the fork body and protect the sliding surface of the inner tube or the oil seal from a foreign object.